Appliances and other machines that generate noise are usually provided with acoustical insulation to reduce the levels of emanating sound. The unwanted sound from these machines can be caused both by the mechanical operation of the motor or other mechanical component within the machine and by the vibration of the machine itself. In a residential dwelling, excessive noise may be generated by dishwashers, clothes washers, clothes dryers, refrigerators, freezers, and microwave ovens, which can be annoying to inhabitants of the dwelling.
Conventional acoustical treatments for machines generally comprises sound transmission barriers and sound absorption layers. One form of acoustical insulation involves enclosing the noise source in an insulation structure. A typical form of acoustical insulation is a layer of mineral fiber insulation, such as fiberglass insulation, wrapped around or positioned around the source of unwanted noise. For example, a fiberglass absorber is usually incorporated in the front door panel of an under-the-counter dishwasher. The blanket of glass fibers absorbs some of the sound energy entering the fiberglass absorber, thereby resulting in a reduced transmission of unwanted sound from the source of sound in the appliance. Further, it is known that the insertion of a reflecting sound barrier within the acoustical insulation also reduces the sound transmission through the insulation product.
Thermoplastic blanket materials are well known in the art. Such materials have been utilized as acoustical and thermal insulators and liners for application to appliances. These insulators and liners typically rely upon both sound absorption, i.e. the ability to absorb incident sound waves and transmission loss, i.e. the ability to reflect incident sound waves, in order to provide sound attenuation. An example of a multilayer thermoplastic blanket having densified layers is disclosed by U.S. Pat. No. 7,357,974, which is incorporated herein by reference in its entirety.